1. Field of The Invention
Methods and apparatuses consistent with the present invention relate to identification (ID) anti-collision and radio frequency identification (RFID) systems. More particularly, the present invention relates to an anti-collision method using a collision bit determination and a RFID system thereof.
2. Description of The Prior Art
RFID technology reads out information from the tags attached to objects via radio waves. RFID is applied to various fields such as product distribution management, security, delivery, and so on. Contact barcode system is replaced by RFID which can read out information much faster. RFID provides advantages such as wide range of operation, and product intelligence.
In a ubiquitous computing environment, multiple tags may come into a reading range of a reader. When the tags respond to a request of the reader at the same time, signals from the tags interfere and collide with one another.
An anti-collision algorithm is adopted to resolve interference between the reply signals of the tags to allow collision-free recognition of the replies from the tags.
Many anti-collision algorithms have been proposed. In one anti-collision algorithm, for example, a binary ID can be provided to a tag so that tags with unintended IDs are eliminated from the consideration. This will be explained briefly below.
First, a (n)-bit binary ID is provided to a tag, and a reader transmits ID request signal to a plurality of tags. The ID request signal includes a ‘0’ or ‘1’ binary ID request value. Upon receiving the ID request signal, each tag compares the ID request value with the first bit of its own ID, and if the data match, transmits its ID to the reader. For example, all the tags with IDs starting with ‘1’, transmit their IDs to the reader in response to ‘1’ ID request value. Likewise, all the tags with IDs starting with ‘0’ transmit their IDs to the reader in response to ‘0’ ID request value.
If one tag responds to the ID request signal, the responding tag is confirmed to be the tag desired by the reader. If more than one tag responds to the reader and first bits of the IDs collide against each other, the reader transmits ‘0’ or ‘1’ binary ID request signal with respect to the next bits of the tag IDs. The reader resets non-responding tags, and thus removes the non-responding tags from the consideration.
If more than one tag responds to the second ID request signal again, the reader transmits another ID request signal with respect to next bits of the IDs. This process repeats until only one tag responds to the ID request signal.
As explained above, conventionally, the reader repeatedly generates and transmits one-bit ID request signal when more than one tags respond. Therefore, it becomes problematic when the collision IDs are composed of many bits because much time is consumed. Additionally, the tags transmit their entire IDs rather than the bits of interest, thereby increasing power consumption.
Therefore, an RF system which operates with requiring reduced time and power, is necessary.